	Introduction

The United States has actively pursued the development of hypersonic weapons as a part of its conventional prompt global strike (CPGS) program since the early 2000s.. (2) An evaluation of the quantity and quality of research on such technology.. Although funding for these programs has been relatively restrained in the past, both the Pentagon and Congress have shown a growing interest in pursuing the development and near-term deployment of hypersonic systems.. As Vice Chairman of the Joint Chiefs of Staff and former Commander of U.S. Strategic Command General John Hyten has stated, hypersonic weapons could enable "responsive, long-range, strike options against distant, defended, and/or time-critical threats [such as road-mobile missiles] when other forces are unavailable, denied access, or not preferred.". As a result, U.S. hypersonic weapons will likely require greater accuracy and will be more technically challenging to develop than nuclear-armed Chinese and Russian systems.. Background

Several countries are developing hypersonic weapons, which fly at speeds of at least Mach 5 (five times the speed of sound), but none have yet introduced them into their operational military forces.. Given the lack of defined mission requirements for hypersonic weapons, it may be challenging for Congress to evaluate the balance of funding for hypersonic weapons programs, enabling technologies, supporting test infrastructure, and hypersonic missile defense.. However, the United States, in contrast to Russia and China, is not currently considering or developing hypersonic weapons for use with a nuclear warhead.. Hypersonic cruise missiles are powered by high-speed, air-breathing engines, or "scramjets," after acquiring their target.. Indeed, as Assistant Director for Hypersonics (USD R&E) Mike White has stated, DOD has not yet made a decision to acquire hypersonic weapons and is instead developing prototypes to "[identify] the most viable overarching weapon system concepts to choose from and then make a decision based on success and challenges.". Issues for Congress

As Congress reviews the Pentagon's plans for U.S. hypersonic weapons programs during the annual authorization and appropriations process, it might consider a number of questions about the rationale for hypersonic weapons, their expected costs, and their implications for strategic stability and arms control.. Mission Requirements

Although the Department of Defense is funding a number of hypersonic weapons programs, it has not established any programs of record, suggesting that it may not have approved requirements for hypersonic weapons or long-term funding plans.. Open-source reporting indicates that both China and Russia have conducted numerous successful tests of hypersonic glide vehicles, and both are expected to field an operational capability as early as 2020 .. Proposed measures include expanding New START, negotiating new multilateral arms control agreements, and undertaking transparency and confidence-building measures.. There are two primary categories of hypersonic weapons
Hypersonic glide vehicles (HGV) are launched from a rocket before gliding to a target.. This approach is reflected in DOD's FY2021 request, which allocates $206.8 million for hypersonic defense programsâof a total $3.2 billion request for all hypersonic-related research.. This is due, in part, to the growing interest in these technologies in Russia and China, leading to a heightened focus in the United States on the strategic threat posed by hypersonic flight.. U.S. Hypersonic Testing Infrastructure114
The United States has actively pursued the development of hypersonic weaponsâmaneuvering weapons that fly at speeds of at least Mach 5âas a part of its conventional prompt global strike program since the early 2000s. In recent years, the United States has focused such efforts on developing hypersonic glide vehicles, which are launched from a rocket before gliding to a target, and hypersonic cruise missiles, which are powered by high-speed, air-breathing engines during flight. As Vice Chairman of the Joint Chiefs of Staff and former Commander of U.S. Strategic Command General John Hyten has stated, these weapons could enable "responsive, long-range, strike options against distant, defended, and/or time-critical threats [such as road-mobile missiles] when other forces are unavailable, denied access, or not preferred." Critics, on the other hand, contend that hypersonic weapons lack defined mission requirements, contribute little to U.S. military capability, and are unnecessary for deterrence.
Funding for hypersonic weapons has been relatively restrained in the past; however, both the Pentagon and Congress have shown a growing interest in pursuing the development and near-term deployment of hypersonic systems. This is due, in part, to the growing interest in these technologies in Russia and China, both of which have a number of hypersonic weapons programs and are expected to field an operational hypersonic glide vehicleâpotentially armed with nuclear warheadsâas early as 2020. The United States, in contrast to Russia and China, is not currently considering or developing hypersonic weapons for use with a nuclear warhead. As a result, U.S. hypersonic weapons will likely require greater accuracy and will be more technically challenging to develop than nuclear-armed Chinese and Russian systems.
The Pentagon's FY2021 budget request for all hypersonic-related research is $3.2 billionâup from $2.6 billion in the FY2020 requestâincluding $206.8 million for hypersonic defense programs. At present, the Department of Defense (DOD) has not established any programs of record for hypersonic weapons, suggesting that it may not have approved either requirements for the systems or long-term funding plans. Indeed, as Assistant Director for Hypersonics (Office of the Under Secretary of Defense for Research and Engineering) Mike White has stated, DOD has not yet made a decision to acquire hypersonic weapons and is instead developing prototypes to assist in the evaluation of potential weapon system concepts and mission sets.
As Congress reviews the Pentagon's plans for U.S. hypersonic weapons programs, it might consider questions about the rationale for hypersonic weapons, their expected costs, and their implications for strategic stability and arms control. Potential questions include the following:
What mission(s) will hypersonic weapons be used for? Are hypersonic weapons the most cost-effective means of executing these potential missions? How will they be incorporated into joint operational doctrine and concepts? Given the lack of defined mission requirements for hypersonic weapons, how should Congress evaluate funding requests for hypersonic weapons programs or the balance of funding requests for hypersonic weapons programs, enabling technologies, and supporting test infrastructure? Is an acceleration of research on hypersonic weapons, enabling technologies, or hypersonic missile defense options both necessary and technologically feasible? How, if at all, will the fielding of hypersonic weapons affect strategic stability? Is there a need for risk-mitigation measures, such as expanding New START, negotiating new multilateral arms control agreements, or undertaking transparency and confidence-building activities?